This invention relates to an image reading apparatus and method (e.g., used with a thermal transfer type copying machine).
Color copying machines of the thermal transfer type are now in widespread use. In the copying machine, a document is scanned to produce an image signal representing the document. The image signal is divided into color component signals. Images of the respective color components are superposedly impressed on a single copy sheet so that a colored copy is obtained.
A description with reference to FIG. 1 of an image reading apparatus used with a conventional thermal transfer type copying machine will now be given. A document D is illuminated by a lamp (not shown). Light reflected from one scanning line of the document is guided to light receiving elements, thereby producing an image signal of a corresponding scanning line as a result of photoelectric conversion. The whole of the document is read, while the lamp and the light receiving elements travel along the document. The light receiving elements are comprised of CCD line sensors.
One CCD line sensor, produced in quantity by a known technique, is shorter than the width of the document, i.e., the length of the scanning line of the document. Therefore, eight CCD line sensors Q1 through Q8 are arranged along a scanning line of the document. The CCD line sensor is comprised of a package and an array of the photosensitive elements contained in the package. The effective of the CCD line sensor is the of the photosensitive elements array and is shorter than that of the package. To ensure the contiguity of the read out image signal, the CCD line sensors Q1 through Q8 are alternately staggered in two rows and each of the sensors overlaps the adjacent two CCD line sensors.
Light reflected from the scanning line is transmitted to CCD line sensors Q1, Q3, Q5 and Q7 of a first row through a light transmission lens R1 and also transmitted to CCD line sensors Q2, Q4, Q6 and Q8 of a second row through a light transmission lens R2. The light transmission lenses R1 and R2 respectively consist of a fiber lens array comprising a plurality of linearly arranged light focusing glass fibers such as a "SELFOC" lens, a trade name of a glass fiber lens manufactured by the Japan Glass Plate Mfg. Co. The two fiber lens arrays R1 and R2 are arranged in the form of an inverted V shape as viewed from the cross section. The optical axes of both lenses R1 and R2 intersect each other on the document D.
Therefore, an image signal corresponding to one scanning line is simultaneously produced from the CCD line sensors even if the CCD line sensors are not arranged in one row. However, difficulties arise from the fact that the optical axes of the two lens arrays R1 and R2 intersect each other on the document D. The optical axes intersect each other on the upper surface of the document table. Therefore, the axes intersect each other on the document so long as the document is flat. If the document is not flat and the document is not placed flush against the document table, the optical axes of the two lens arrays are directed towards different scanning lines of the document and consequently each row of the CCD line sensors, Q1 through Q8 staggered in two rows, reads out a different scanning line. Therefore, it sometimes happens that an original straight line of document is copied in a zigzag form.
Furthermore, it is difficult to exactly intersect two optical axes at the upper surface of the document table. The precision of the optical axis of the fiber lens arrays R1 and R2 generally involves some errors. Therefore, it is necessary to perform various adjustment operations after the assembly of an image reading apparatus. For instance, the lens arrays are horizontally and vertically moved to adjust the intersecting angle of both lines of the letter V formed by the axes of the lens arrays R1 and R2. This adjustment work consumes a great deal of time and labor.